Hello, Sergey,

thanks for the patch! LGTM with a minor comment.

From: Mike Pall <mike>

(cherry picked from commit de6b1a11dd1a3349179084578c5d533be1c30234)

Before this patch, Valgrind produces tons of warnings during the VMevent
calls since the `IR_NOP` instruction isn't fully initialized. Hence, any
parsing operations for it in handlers during `jit.dump()` leads to the
"uninitialised value" error. This patch fixes the issue by the proper
init of such IRs.

Please add to a comment that with these tests the problem could

 be reproduced:

test/tarantool-tests/lj-1128-table-new-opt-tnew.test.lua

test/tarantool-tests/fix-jit-dump-ir-conv.test.lua

test/tarantool-tests/unit-jit-parse.test.lua

Sergey Kaplun:
* added the description for the problem

Needed for tarantool/tarantool#3705
Part of tarantool/tarantool#10709
---
 src/lj_asm.c     |  2 +-
 src/lj_ir.h      |  8 ++++++++
 src/lj_opt_dce.c |  5 +----
 src/lj_opt_mem.c | 25 +++++--------------------
 4 files changed, 15 insertions(+), 25 deletions(-)

diff --git a/src/lj_asm.c b/src/lj_asm.c
index 5137d05c..f7540165 100644
--- a/src/lj_asm.c
+++ b/src/lj_asm.c
@@ -2377,7 +2377,7 @@ void lj_asm_trace(jit_State *J, GCtrace *T)
   /* Ensure an initialized instruction beyond the last one for HIOP checks. */
   /* This also allows one RENAME to be added without reallocating curfinal. */
   as->orignins = lj_ir_nextins(J);
-  J->cur.ir[as->orignins].o = IR_NOP;
+  lj_ir_nop(&J->cur.ir[as->orignins]);
 
   /* Setup initial state. Copy some fields to reduce indirections. */
   as->J = J;
diff --git a/src/lj_ir.h b/src/lj_ir.h
index 27c66f63..46e7413e 100644
--- a/src/lj_ir.h
+++ b/src/lj_ir.h
@@ -587,4 +587,12 @@ static LJ_AINLINE int ir_sideeff(IRIns *ir)
 
 LJ_STATIC_ASSERT((int)IRT_GUARD == (int)IRM_W);
 
+/* Replace IR instruction with NOP. */
+static LJ_AINLINE void lj_ir_nop(IRIns *ir)
+{
+  ir->ot = IRT(IR_NOP, IRT_NIL);
+  ir->op1 = ir->op2 = 0;
+  ir->prev = 0;
+}
+
 #endif
diff --git a/src/lj_opt_dce.c b/src/lj_opt_dce.c
index 6948179c..41e36d99 100644
--- a/src/lj_opt_dce.c
+++ b/src/lj_opt_dce.c
@@ -46,10 +46,7 @@ static void dce_propagate(jit_State *J)
       irt_clearmark(ir->t);
     } else if (!ir_sideeff(ir)) {
       *pchain[ir->o] = ir->prev;  /* Reroute original instruction chain. */
-      ir->t.irt = IRT_NIL;
-      ir->o = IR_NOP;  /* Replace instruction with NOP. */
-      ir->op1 = ir->op2 = 0;
-      ir->prev = 0;
+      lj_ir_nop(ir);
       continue;
     }
     pchain[ir->o] = &ir->prev;
diff --git a/src/lj_opt_mem.c b/src/lj_opt_mem.c
index c9f1216c..a6e9a072 100644
--- a/src/lj_opt_mem.c
+++ b/src/lj_opt_mem.c
@@ -375,10 +375,7 @@ TRef LJ_FASTCALL lj_opt_dse_ahstore(jit_State *J)
 	    goto doemit;  /* No elimination possible. */
 	/* Remove redundant store from chain and replace with NOP. */
 	*refp = store->prev;
-	store->o = IR_NOP;
-	store->t.irt = IRT_NIL;
-	store->op1 = store->op2 = 0;
-	store->prev = 0;
+	lj_ir_nop(store);
 	/* Now emit the new store instead. */
       }
       goto doemit;
@@ -479,10 +476,7 @@ TRef LJ_FASTCALL lj_opt_dse_ustore(jit_State *J)
 	    goto doemit;  /* No elimination possible. */
 	/* Remove redundant store from chain and replace with NOP. */
 	*refp = store->prev;
-	store->o = IR_NOP;
-	store->t.irt = IRT_NIL;
-	store->op1 = store->op2 = 0;
-	store->prev = 0;
+	lj_ir_nop(store);
 	if (ref+1 < J->cur.nins &&
 	    store[1].o == IR_OBAR && store[1].op1 == xref) {
 	  IRRef1 *bp = &J->chain[IR_OBAR];
@@ -491,10 +485,7 @@ TRef LJ_FASTCALL lj_opt_dse_ustore(jit_State *J)
 	    bp = &obar->prev;
 	  /* Remove OBAR, too. */
 	  *bp = obar->prev;
-	  obar->o = IR_NOP;
-	  obar->t.irt = IRT_NIL;
-	  obar->op1 = obar->op2 = 0;
-	  obar->prev = 0;
+	  lj_ir_nop(obar);
 	}
 	/* Now emit the new store instead. */
       }
@@ -585,10 +576,7 @@ TRef LJ_FASTCALL lj_opt_dse_fstore(jit_State *J)
 	    goto doemit;  /* No elimination possible. */
 	/* Remove redundant store from chain and replace with NOP. */
 	*refp = store->prev;
-	store->o = IR_NOP;
-	store->t.irt = IRT_NIL;
-	store->op1 = store->op2 = 0;
-	store->prev = 0;
+	lj_ir_nop(store);
 	/* Now emit the new store instead. */
       }
       goto doemit;
@@ -839,10 +827,7 @@ TRef LJ_FASTCALL lj_opt_dse_xstore(jit_State *J)
 	    goto doemit;  /* No elimination possible. */
 	/* Remove redundant store from chain and replace with NOP. */
 	*refp = store->prev;
-	store->o = IR_NOP;
-	store->t.irt = IRT_NIL;
-	store->op1 = store->op2 = 0;
-	store->prev = 0;
+	lj_ir_nop(store);
 	/* Now emit the new store instead. */
       }
       goto doemit;